<template>
  <div class="pagination">
    <button :disabled="pageNo==1" @click="$emit('getPageNo',pageNo-1)">上一页</button>
    <button v-if="satrtNumAndEndNum.start>1" @click="$emit('getPageNo', 1)" :class="{active:pageNo==1}">1</button>
    <button v-if="satrtNumAndEndNum.start>2">···</button>

    <!-- 中间结构 -->
    <button v-for="(page, index) in satrtNumAndEndNum.end" 
            :key="index" v-if="page>=satrtNumAndEndNum.start" 
            @click="$emit('getPageNo', page)"
            :class="{active:pageNo==page}"
    >
        {{page}}
    </button>
    
    <button v-if="satrtNumAndEndNum.end<totalPage - 1">···</button>
    <button v-if="satrtNumAndEndNum.end<totalPage" @click="$emit('getPageNo', totalPage)" :class="{active:pageNo==totalPage}">{{totalPage}}</button>
    <button :disabled="pageNo==totalPage" @click="$emit('getPageNo',pageNo+1)">下一页</button>
    
    <button style="margin-left: 30px">共 {{total}} 条</button>
  </div>
</template>

<script>
  export default {
    name: "Pagination",
    props:['pageNo', 'pageSize', 'total', 'continues'],
    //计算属性
    computed:{
        //计算总共多少页 向上取整
        totalPage(){
            return Math.ceil(this.total / this.pageSize)
        },
        //计算出连续的页码的起始数字和结束数字【连续的页码数至少是5】
        satrtNumAndEndNum(){
            const {continues, pageNo, totalPage} = this
            //定义两个变量存储：起始数字与结束数字
            let start = 0;
            let end = 0;
            //连续页码数字5【就是至少5页】，如果出现不正常的现象【就是不够5页】
            if(continues > this.totalPage){
                //不正常现象，总页数不够5页
                start = 1
                end = totalPage
            }else {
                //正常现象，连续页数为5，且总页数大于5
                start = pageNo - parseInt(continues/2)
                end = pageNo + Math.floor(continues/2)
                // 把出现不正常的现象【start数字为 0 或者 负数】纠正
                if(start < 1){
                    start = 1
                    end = continues
                }
                // 把出现不正常的现象【end数字大于总页码 totalPage】纠正
                if(end > totalPage){
                    end = totalPage
                    start = totalPage - continues + 1
                }
            }
            return {start, end}
        }
    }
  }
  
</script>

<style lang="less" scoped>
  .pagination {
    text-align: center;
    button {
      margin: 0 5px;
      background-color: #f4f4f5;
      color: #606266;
      outline: none;
      border-radius: 2px;
      padding: 0 4px;
      vertical-align: top;
      display: inline-block;
      font-size: 13px;
      min-width: 35.5px;
      height: 28px;
      line-height: 28px;
      cursor: pointer;
      box-sizing: border-box;
      text-align: center;
      border: 0;

      &[disabled] {
        color: #c0c4cc;
        cursor: not-allowed;
      }

      &.active {
        cursor: not-allowed;
        background-color: #409eff;
        color: #fff;
      }
    }
  }
  .active{
    background: skyblue;
  }
</style>
